Weakest digital link: DAC - Streamer - Server?

I am curious WHICH of the three is MOST important in digital playback? DAC, Streamer, or Server? I assume DAC is #1, but what about server/streamer?

Specifically, I have a Synology NAS which I can host ALL my music on, then using a good streamer play off it via Roon/Upnp, PLUS my streaming services.  Does it make sense to use a SEPARATE server JUST for my music? 

Like is there going to be MUCH difference between these setups?!

1. NAS (music server) --> Good Streamer (ethernet, Roon) --> DAC

2. Dedicated Music Server --> Same streamer (ethernet, Roon) --> DAC

3. Dedicated Music Server with streamer (digital out) --> DAC

I understand for SURE, if one connects a NAS USB out to streamer/DAC it will sound WORSE than dedicated music server with low noise components, BUT if I am sending the music over ethernet to a good streamer, WHY would a music server make ANY difference? The streamer would essentially take the same files off my NAS, as if would from Tidal and play in the same fashion... no?! 

WHAT am I missing?!

PS. I can also upgrade the NAS with linear PSU to lower noise, but once again, sending audio through ethernet shouldn't matter.